1. Field of the Invention
The present invention relates to an image recording apparatus for effecting image recording in response to input image signals.
2. Description of the Prior Art
Recording apparatus equipped with plural recording elements such as light-emitting diodes, liquid crystal display elements or needle electrodes has been recently employed as an output unit for facsimile reception or for computer. As an example of such apparatus, FIG. 1 shows an electrostatic recording apparatus equipped with needle electrodes, wherein an electroconductive drum 1 provided with a dielectric surfacial layer is surrounded by a primary charger 2 for uniformly charging said dielectric layer positively; a stylus head 3 provided with plural needle electrodes arranged in the axial direction of said drum over the entire width thereof for applying a negative voltage to said positively charged dielectric layer to form an electrostatic latent image thereof; a developing station 4 for developing said electrostatic latent image on means of dielectric layer into a visible image by the toner deposition; a transfer charger 5 for transferring thus formed toner image onto a recording sheet 7; and a cleaning station 6 for removing the toner remaining on the dielectric layer after image transfer.
In such apparatus the drum 1 is rotated in the direction indicated by an arrow at a constant speed, and a positive voltage of several hundred volts is supplied to the primary charger 2 to uniformly charge said dielectric layer to a positive potential. Image signals representing characters, symbols, patterns, etc., obtained as facsimile reception signals or as computer output signals are converted, in a stylus driver 11, into negative pulse voltages of several hundred volts and supplied to the needle electrodes of the stylus head 3, thereby eliminating the positive charge in the positions corresponding to such characters, symbols or patterns, thus forming an electrostatic latent image. Upon further rotation of the drum 1 as indicated by the arrow, the electrostatic latent image is developed into a visible image in the developing station 4 by the deposition of toner particles, for example from a magnetic brush, charged to a polarity opposite to that of the latent image. Subsequently said visible image is rotated to the position of the transfer charger 5, where the visible image is transferred, by means of corona discharge, onto the recording sheet 7 supplied by a feed roller 8 and transport rollers 10. Then the recording sheet 7 is transferred to fixing rollers 9 for fixing said transferred image onto the recording sheet 7 under heat and pressure, and the drum 1 is subjected to the removal of remaining toner in the cleaning station 6 in order to prepare said drum for the succeeding recording cycle.
As shown in FIG. 2, the stylus head 3 is provided with a plurality of needle electrodes 2-1 arranged at a density of 4 to 16 electrodes/mm in order to achieve recording of high resolution. For achieving simultaneous recording with such high-density stylus head 3, for example over a short end of B4 size (256.times.364 mm), there will be required 4096 needle electrodes at a density of 16 electrodes/mm. Formation of an electrostatic latent image by supplying negative pulse voltages in the order from -200 to -300 volts to the needle electrodes of such large number requires an enormous number of high-voltage transistors and latch circuits.
Consequently it has recently been common to employ plural units of a high-voltage resistant MOS-IC which can be directly connected to TTL circuits and incorporates, as shown in FIG. 3, a shift register 3-1, a latch circuit 3-2, several tens of AND gates 3-3-1-3-3-n and high-voltage MOS field effect transistors 3-4-1-3-4-n, with the operating procedure as described in the following.
Time-sequential image signals are supplied from a data input terminal DIN(1) and stored in the shift register 3-1 driven by clock signals supplied from a clock input terminal CK(2). After said storage, said signals are read in parallel manner, stored in the latch circuit 3-2 driven by a latch signal supplied from a latch input terminal LS(4), then again read in parallel manner and supplied to the high-voltage MOSFET 3-4-1-3-4-n through the AND gates 3-3-1-3-3-n, thereby obtaining high-voltage output image signals from output terminals OUT(6)-OUT(n+5) in parallel manner. The image signals from the shift register 3-1 can be read, when required, from a data output terminal DOUT(3). Also said AND gates are opened by a clear signal from an input terminal CL(5) and intercept the transmission of image signals when they are not needed.
Such high-voltage resistant MOS-IC may contain 8 to 32 units of MOSFET's as an integrated circuit, but, in order to drive 4096 needle electrodes provided at a density of 16 electrodes/mm on the stylus head 3 for B4 size recording, there will be required 128 units of such MOS-IC, each incorporating 32 integrated MOSFET's, to be serially connected.
However the signal processing speed of such MOS-IC is significantly lower than that of TTL circuits and can be in the order of 4 MHz at maximum. At the signal processing speed of 4 MHz, the time required for entering the serial image signals of a line into thus serially connected MOS-IC's for driving the stylus head with 4096 needle electrodes will be: EQU 4096.times.1/4 MHz=ca. 1 msec.
which therefore results in a time of ca. 1.5 milliseconds per line in consideration of the driving time required for FET's. Thus the recording of B4 size, including 5824 lines in the longer side at a density of 16 lines/mm, will require 1.5 msec..times.5824=8.7 seconds. For this reason a high-speed recording cannot be expected with the conventional technology.
Also in the recording apparatus of other types, an increase in the quantity of image signals per line leads to an increase in the time required for the entry of image signals for driving the recording elements, thus giving rise to a loss in the recording speed or to a loss in the output speed of image signals according to the recording speed of said recording apparatus.